This works as long as they don't insist on verifying you through that secondary phone number (this is the case for now for Google I think - if something suspici

This works as long as they don't insist on verifying you through that secondary phone number (this is the case for now for Google I think - if something suspicious is going on, they ask you if you want an sms with a verification code, or an email to a secondary address; but maybe not all services with 2FA make this optional). It's not fun to have 2 phones always with you. But maybe the 2-SIM devices will become more mainstream soon, which can solve this problem.